1. Field of the Invention
The present invention relates to selected liquid, radiation-curable compositions which are particularly suitable for the production of three-dimensional articles by stereolithography as well as a process for the production of cured articles and the cured three-dimensional shaped article themselves. In particular, this invention relates to a liquid, radiation-curable resin compositions from which cured three-dimensional shaped articles having very high impact resistance characteristic of ABS resins can be made.
2. Brief Description of Art
The production of three-dimensional articles of complex shape by means of stereolithography has been known for a relatively long time. In this technique the desired shaped article is built up from a liquid, radiation-curable composition with the aid of a recurring, alternating sequence of two steps (a) and (b); in step (a), a layer of the liquid, radiation-curable composition, one boundary of which is the surface of the composition, is cured with the aid of appropriate radiation, generally radiation produced by a preferably computer-controlled laser source, within a surface region which corresponds to the desired cross-sectional area of the shaped article to be formed, at the height of this layer, and in step (b) the cured layer is covered with a new layer of the liquid, radiation-curable composition, and the sequence of steps (a) and (b) is repeated until a so-called green model of the desired three-dimensional shape is finished. This green model is, in general, not yet fully cured and must therefore, normally, be subjected to post-curing.
The mechanical strength of the green model (modulus of elasticity, fracture strength), also referred to as green strength, constitutes an important property of the green model and is determined essentially by the nature of the stereolithographic-resin composition employed. Other important properties of a stereolithographic resin composition include a high sensitivity for the radiation employed in the course of curing and a minimum curl factor, permitting high shape definition of the green model. In addition, for example, the precured material layers should be readily wettable by the liquid stereolithographic resin composition, and of course not only the green model but also the ultimately cured shaped article should have optimum mechanical properties.
In order to achieve the desired balance of properties, different types of resin systems have been proposed. For example, radical-curable resin systems have been proposed. These systems generally consist of one or more (meth)acrylate compounds (or other free-radical polymerizable organic compounds) along with a free-radical photoinitiator for radical generation. U.S. Pat. No. 5,418,112 describes one such radical-curable system.
Another type of resin composition suitable for this purpose is a dual type system that comprises (i) epoxy resins or other types of cationic polymerizable compounds; (ii) cationic polymerization initiator; (iii) acrylate resins or other types of free radical polymerizable compounds; and (iv) a free radical polymerization initiator. Examples of such dual or hybrid systems are described in U.S. Pat. No. 5,434,196.
A third type of resin composition useful for this application also includes (v) hydroxyl-containing compounds such as polyether-polyols. Examples of such hybrid systems are described in U.S. Pat. Nos. 5,972,563; 6,100,007 and 6,287,748.
Separately, epoxy interpenetrating polymer networks or so-called toughened epoxy resins such as Taxtic 695 (commercially available from Vantico, Inc. of Brewster, N.Y.) have been used alone or in additives to other resins to increase toughness. Epoxy interpenetrating polymer networks (called an EPRXE resin wherein a diepoxy resin is involved) resins containing epoxy functions along with other moieties. Taxtic 695 is a particular EPRXE resin and its formula is shown on columns 10 and 11 of U.S. Pat. No. 5,360,877. In the past, these resins were cured with a variety of amine and anhydride-based curing agents. It is believed such toughened epoxy resins have not been used in stereolithographic resin applications.
Despite all previous attempts, there exists a need for a liquid hybrid stereolithographic composition capable of producing cured articles that possess very high impact resistance characteristic of ABS resins along with other mechanical and chemicals desired in stereolithographic resins. The present invention presents a solution to that need.
Therefore, one aspect of the present invention is directed to a liquid radiation-curable composition useful for the production of three dimensional articles by stereolithography that comprises
(A) at least one cationically polymerizing organic substance;
(B) at least one free-radical polymerizing organic substance;
(C) at least one cationic polymerization initiator;
(D) at least one free-radical polymerization initiator;
(E) at least one hydroxyl-functional compound; and
(F) at least one epoxy interpenetrating polymer compound.
Another aspect of the present invention is directed to a process for forming a three-dimensional article, said process comprising the steps:
(1) coating a thin layer of a radiation-curable composition onto a surface;
(2) exposing said thin layer imagewise to actinic radiation to form an imaged cross-section, wherein the radiation is of sufficient intensity to cause substantial curing of the thin layer in the exposed areas;
(3) coating a thin layer of the composition onto the previously exposed imaged cross-section;
(4) exposing said thin layer from step (3) imagewise to actinic radiation to form an additional imaged cross-section, wherein the radiation is of sufficient intensity to cause substantial curing of the thin layer in the exposed areas and to cause adhesion to the previously exposed imaged cross-section;
(5) repeating steps (3) and (4) a sufficient number of times in order to build up the three-dimensional article;
wherein the radiation-curable composition is that which is described above.
Still another aspect of the present invention is directed to three-dimensional articles made by the above process using the above-noted radiation-curable composition.
It is an advantage that the liquid radiation-curable composition of the present invention provides parts with high modulus of flexure and tensile when used in a stereolithography system to form a three-dimensional object.
It is another advantage that the liquid radiation-curable composition of the present invention provides parts with good elongation to break and which are not brittle when used in a stereolithography system to form a three-dimensional object.
It is yet another advantage that the liquid radiation-curable composition of the present invention provides parts with stable properties in the presence of moisture when used in a stereolithography system to form a three-dimensional object.
It is still another advantage that the liquid radiation-curable composition of the present invention provides a resin material that permits a reliable process to produce high quality three-dimensional parts to be easily designed.